Her flippant attitude toward matches is wearing thin and it's time for Stephens to grow up.

Stephens' 1-6, 0-6 loss to Caroline Wozniacki on Sunday evening at the Sony Miami Open was worse than embarrassing. It was disrespectful to the people who paid to see a tennis match. Instead, what they got was another petulant performance by the WTA's resident brat.

Despite turning 21 on March 20, Stephens sometimes behaves like a toddler. When things aren't going her way, she packs up her game and goes home.

The problem is she does this during a match when there are plenty of points to be played.

Stephens displayed perhaps the most unforgivable attitude you'll ever get from a professional athlete: indifference. She was so apathetic in her pathetic performance, that tennis commentators criticized her on the air and via Twitter.

Wozniacki deserves some credit for remaining poised while playing someone so seemingly disinterested in the match. She dismissed Stephens in 55 minutes. For those watching, it was 55 woeful minutes of a professional player against someone playing professional tennis.

Young players turning in poor performances is nothing new. Earlier in the day Madison Keys squandered a chance to go up 3-0 in the second set against No. 2 Li Na. Keys showed lack of experience and confidence.

Stephens, however, displayed lack of commitment. She acted as if the match was some annoying appointment on her schedule. She had 37 unforced errors and at times appeared detached from the match. Down 6-1, 4-0 in the second set, Stephens served what she thought was a fault.

Yet, it wasn't called. Wozniacki blasted a return right past Stephens who just stood there, looking silly. Even recreational players understand you play the point regardless of whether you think your serve is long.

Recently, Stephens registered with Target for her 21st birthday. Despite career earnings of more than $2.4 million and at least a million more in endorsement deals, Stephens filled out a bridal registry that included a lengthy wish list. Unless Target sells the heart of a champion, it's doubtful Stephens will get everything she needs.

Stephens could learn from 33-year-old Venus Williams, who in contrast, showed us why she has 45 career singles titles. Stephens has none and has yet to reach a singles final. Fighting the Florida heat and a chronic illness, Williams battled for every point.

Not even the great Paul Annacone could coach Sloane Stephens through a miserable match.Matthew Stockman/Getty Images

After edging Casey Dellacqua in three sets, Williams told Tennis.com's Peter Bodo that she never goes out without a fight. “If I go down it's never easy. At least my opponent knows they have to go to the end of the earth to take me out no matter what the circumstances, usually."

That's how champions think.

Stephens, on the other hand, had few answers for her lackluster performance. In her post-match press conference, Stephens basically told reporters it just wasn't her night. "Not really anything I'm going to cry too much over. I'm just going to get back to work and get ready for Charleston next week."

It's hard to know if what Stephens shows on the court is what she's actually feeling. Perhaps she has a stellar work ethic and just has a difficult time handling pressure. However, what fans see too often is Stephens sulking, shrugging and literally dragging her feet from one point to the next.

In an article written for ESPN The Magazine, writer Howard Bryant compared Stephens' rise and descent to the career of Washington Redskins quarterback Robert Griffin III. Bryant cautioned "that being declared "It" is at best a cruel trap; it's to be treated like a legend without actually being one, then to be rebuked severely when expectations are not met."

Yet, losing seems to bother RGIII. Even in his worst defeats, Griffin never appeared disinterested in the outcome.

Stephens is young and has time to make attitude adjustments. But more matches like this raises more questions about her future. Does she have the inner fortitude to win a title? Has she fallen prey to the pressure of the hype? Will she ever grow up?